FIG. 5 is a sectional view showing an example of a conventional LED lamp (see, for example, Patent Document 1). The LED lamp X shown in the figure includes an elongated rectangular-shaped substrate 91, a plurality of LEDs 92 mounted on the substrate 91, a tube 93 that accommodates the substrate 91, a terminal 94, and a circuit 95 for turning on the LEDs 92. On the substrate 91, a wiring (not shown) is provided that connects the plurality of LEDs 92 and the terminal 94. The LED lamp X is configured to turn on the plurality of LEDs 92 upon fitting the terminal 94 to a socket of a general-purpose fluorescent illumination instrument. Since LEDs 92 have lower power consumption and a longer life, to use the LED lamp X as a substitute for a fluorescent lamp is expected to provide advantage in cost and environment.
Herein, the general-purpose fluorescent illumination instrument refers to an illumination instrument mainly used for general interior illumination, more specifically to an illumination instrument that utilizes, for example in Japan, the commercial power supply of 100 V, and is compatible with a straight-tube fluorescent lamp according to JIS C7617 or a circular fluorescent lamp according to JIS C7618.
In the case of a straight-tube fluorescent lamp for use with a general-purpose fluorescent illumination instrument, FL 20W lamps, which have a shorter tube length (580 mm), and FL40W lamps, which have a longer tube length (1198 mm), for example, are specified to use the same type of base in common.
In the case of the conventional LED lamp X, however, such two types of lamps having different lengths are manufactured as completely different products, with difference in length of the substrate 91 as well as in the number of LEDs 92 mounted on the substrate 91. This considerably raises the manufacturing cost, and complicates the management of the products.    Patent Document 1: JP-U-H06-54103